An optical fiber generally includes a core region and a cladding region, and may also include one or more coatings over the cladding region. Optical fibers may be bundled within tubing to form a cable. Meeting optical signal-to-noise ratio (OSNR) requirements for advanced modulation schemes employed in long-haul optical cable transmission system, such as submarine cable transmission systems, may require high signal power. However, high signal power may result in nonlinear propagation impairments. Providing a fiber with a high effective area (Aeff) is one way to help minimize nonlinear propagation impairments. However, the potential for microbending-related signal attenuation generally increases with increasing effective area.
High packing density is generally desirable in optical cables. Packing density is the ratio of the total cross-sectional area of the fibers (including coatings) to the cross-sectional area of the tubing interior in which the fibers are contained. The potential for excess microbending-related signal attenuation generally increases with increasing packing density, due to mechanical interaction among the fibers contained within the tube and related effects. Accordingly, minimizing the total coated fiber diameter can help keep the packing density low as the number of fibers within a cable is increased. For reasons including that a relatively large effective area may be desired and that the diameters of the glass (core and cladding) portions of a fiber are relatively standardized, it is generally undesirable to reduce those diameters. Therefore, fibers having relatively large effective area but with reduced coating thickness have been developed. However, such reduced-thickness coating fibers may nevertheless suffer from unacceptable microbending-related signal attenuation.
Coating properties may be carefully selected to help mitigate the undesirable effects of microbending. Coating a fiber with a thick layer of material with a low modulus of elasticity (also referred to as Young's modulus) may provide a “cushioning” layer with low lateral rigidity that may reduce the mechanical perturbations to the fiber axis that produce microbending loss. However, such a low modulus coating material may easily be damaged during the normal handling associated with fiber and cable manufacturing. For this reason, a composite dual-layer coating system, comprising an inner or “primary” coating of low modulus material with low lateral rigidity paired with an outer or “secondary” coating of high modulus material with high flexural stiffness, may help minimize microbend sensitivity while promoting resistance to damage during the normal handling associated with fiber and cable manufacturing.